This invention relates generally to gun-launched projectiles and more particularly to a high-temperature obturator for a gun-launched projectile.
When launching projectiles out of large military guns or cannons, the typical loading technique is to first ram the projectile into the breach of the gun, and then to ram a propelling charge in a shell casing behind the projectile. The propelling charge is typically positioned in the breach by a shell casing rim that is similar to the rim on a bullet cartridge used with a handgun. This rim is larger than the diameter of the breach and is prevented from being inserted into the barrel of the gun.
Projectiles launched from military guns are typically rear obturated. The aft end of the projectile has a protruding ring or flange of material called an obturator or a rotating band. The obturator has a diameter smaller than the diameter of the breach, but larger than the diameter of the bore of the gun barrel. The bore is the section of the barrel that typically contains a series of rifling grooves used to impart a spin on the projectile.
During loading, the projectile is rammed into the breach in a manner similar to putting a bullet in a gun chamber. However, unlike a typical bullet, the projectile does not have a cartridge rim to stop it (only the separate propelling charge has a cartridge rim). Therefore, the aft end or rear obturator is used to stop the projectile once it has traveled an appropriate distance into the barrel. Because the rear obturator has a diameter larger than the bore diameter of the gun, the obturator is stopped during loading of the projectile in an area of the gun barrel where the inside diameter decreases from the breach diameter to the bore diameter. This area of inside diameter change is called the forcing cone. Because the obturator is located at the rear of the projectile, when the obturator stops at the forcing cone, most of the projectile is positioned in the bore of the barrel.
When the propelling charge is ignited, the rear of the projectile is forced into the bore of the gun barrel. The obturator, which has a diameter larger than the bore of the gun, is forced to extrude into the rifling grooves. This extrusion helps to prevent the charge gases created by the ignition of the propelling charge from flowing past the projectile in the rifling grooves. By preventing the charge gases from blowing by the projectile, the obturator causes the charge gases to drive the projectile out of the gun at the optimal velocity. In addition, since the rifling grooves spiral down the barrel, the grooves impart a spin to the projectile to increase flight stability.
Advanced projectiles (xe2x80x9csmartxe2x80x9d projectiles) are capable of being fired from the same guns that are used to fire the standard unguided projectiles described above. An example of an unguided projectile is a standard artillery shell, which is basically an oversized bullet. On the other hand, advanced projectiles have enhanced features such as electronic guidance and extended range rocket motors. For example, certain advanced projectiles are launched from a gun using a propelling charge, but then use a rocket motor and a guidance system to propel them to a selected target. These advanced projectiles must be designed to be loaded and fired in the same gun barrels that were designed to fire the standard unguided projectiles. However, advanced projectiles are often three to four times longer than standard projectiles due to their increased complexity. Because of this increased length, if a standard rear obturator is used on such projectiles, the launch pressures created when the charge is ignited would buckle the aft portion of the advanced projectile.
An obturator or related device must be used in order to stop the charge gases from blowing by the projectile. This function is important in the case of advanced projectiles due to the sensitivity of the guidance electronics. Any blow-by could potentially destroy the projectile""s operability. Additionally, a ramming brake is needed to stop the projectile when it is rammed into the gun. Traditionally, both of these functions have been performed by the rear obturator or rotating band, as described above. However, since the obturator cannot be located at the rear of the projectile on an advanced projectile, the standard rear obturator/rotating band is design used with unguided projectiles must be replaced by one or more components that serve the function of preventing or reducing the blow-by of charge gases during launch of the projectile.
Accordingly, a need has arisen for an obturator for use in conjunction with a gun-launched projectile that functions to prevent or reduce the blow-by of charge gases during the launching of the projectile. The present invention provides a high-temperature obturator for a gun-launched projectile that addresses this need.
According to one embodiment of the present invention, an obturator is provided for a projectile launched from a gun barrel. The obturator includes an annular ring that is fabricated from a high-temperature resistant composite material. The annular ring has an inner surface that is in contact with the projectile. In addition, when the projectile is fired from the gun barrel, an outer surface of the annular ring contacts an inner surface of a bore of the gun barrel. When the projectile is fired from the gun barrel, the radial distance between the inner surface and the outer-surface of the annular ring substantially equals or exceeds the radial distance between an outer surface of the projectile and the inner surface of the bore of the gun barrel at at least one point. This configuration restricts a flow of charge gases from an aft end of the projectile to a forward end of the projectile as the projectile is fired from the gun barrel.
Embodiments of the invention provide numerous technical advantages. For example, in one embodiment of the invention, a obturator is provided that operates to impede the flow of charge gases past the projectile in the gun barrel, even though the obturator may be positioned at a mid-body location on the projectile. This functionality is due, in part, to the ability of the obturator to withstand high temperatures existing in the barrel prior to launch. Such a mid-body obturator is typically needed when used in conjunction with extended-length projectiles. Furthermore, obturators incorporating the teachings of the present invention, whether positioned mid-body or elsewhere on the projectile, are lightweight and will break apart upon exiting the gun barrel. The low weight prevents interference with the operation of the projectile, while the break-up and low mass reduce collateral damage to people and equipment in the vicinity of the gun.
Other technical advantages are readily apparent to one skilled in the art from the following figures, descriptions, and claims.